The IEEE (Institute of Electrical and Electronics Engineers) 802.16 working group is creating an 802.16m radio interface specification that satisfies requirements of an IMT (International Mobile Telecommunications)-advanced next-generation mobile phone system. Based on the IEEE 802.16m draft standard, the WiMAX (Worldwide Interoperability for Microwave Access) forum is working out the WiMAX release 2.0 MSP (Mobile System Profile; mobile communication system profile) (see NPL 1). The IEEE 802.16m standard and WiMAX release 2.0 MSP are expected to be completed by early 2011.
The IEEE802.16 working group has also started envisioning and designing a future 802.16/WiMAX network which excels 802.16m/WiMAX2.0. There is common recognition among the 802.16/WiMAX community that the future 802.16/WiMAX will support an explosive increase of mobile communication data traffic spurred by apparatuses with greater screens, multimedia applications and an increasing number of connected users and apparatuses. The future 802.16/WiMAX network will also efficiently cooperate with other wireless techniques such as 802.11/Wi-Fi (Wireless Fidelity).
The future 802.16/WiMAX network will be drastically improved regarding various performance index values such as throughput and SE (Spectral Efficiency) compared to the 802.16m network. For example, when coverage in a metropolitan area is assumed, the future 802.16/WiMAX network is aiming at SE at a cell edge twice that of the 802.16m/WiMAX2.0 network on both UL (uplink) and DL (downlink) (see NPL 2). It should be noted that the 802.16m/WiMAX2.0 network has SE at a cell edge of at least 0.06 bps/Hz/sec of DL in a 4×2 antenna configuration and SE at a cell edge of at least 0.03 bps/Hz/see of UL in a 2×4 antenna configuration.
For example, collaboration techniques such as CliCo (Client Collaboration) has assured a drastic improvement in SE at a cell edge and energy efficiency of an entire network of a radio communication system. CliCo is a technique for clients to jointly transmit/receive data in radio communication (see NPL 3). CliCo uses client clustering and peer-to-peer communication to transmit/receive information through a plurality of paths between a BS and a client. As a result, it is possible to improve SE at a cell edge without any increase in infrastructure costs. Furthermore, CliCo can extend the service life of a battery of a client having a poor channel.
FIG. 1 shows a diagram illustrating typical radio communication system 100 that performs CliCo. Radio communication system 100 includes BS (base station) 102 and a plurality of MSs (mobile stations), for example MS 104 and MS 106.
FIG. 2 is a block diagram illustrating typical BS 102. BS 102 is equipped with only WiMAX and is constructed of WiMAX PHY block 130 and WiMAX MAC block 120. WiMAX MAC block 120 performs a WiMAX OFDMA (Orthogonal Frequency Division Multiple Access)-based media access control protocol. WiMAX PHY block 130 performs the WiMAX OFDMA-based physical layer protocol under the control of WiMAX MAC block 120.
Referring to FIG. 2, WiMAX MAC block 120 is further constructed of control section 122, scheduler 124, message creation section 126 and message processing section 128.
Control section 122 controls a general MAC protocol operation. Scheduler 124 schedules allocation of resources to each MS under the control of control section 122. Upon receiving resource allocation scheduling information from scheduler 124, message creation section 126 creates a data packet and DL control signaling. Message processing section 128 analyzes the data packet and UL control signaling received from the plurality of MSs under the control of control section 122 and reports the analysis result to control section 122.
It should be noted that the data packet and DL control signaling created by message creation section 126 are transmitted to the plurality of MSs by BS 102 via OFDMA transmitter 136 in WiMAX PHY block 130. The data packet and UL control signaling analyzed by message processing section 128 is received by BS 102 via OFDMA receiver 138 in WiMAX PHY block 130.
Referring to FIG. 2, message creation section 126 includes HFBCH (HARQ Feedback Channel) creation section 132 and resource allocation creation section 134. Here, HARQ represents a hybrid automatic repeat request. HFBCH creation section 132 creates a HARQ feedback channel for UL data transmission that carries HARQ feedback information (e.g., ACK/NACK) for UL data transmission. Resource allocation creation section 134 creates resource allocation control signalling for UL/DL data transmission that carries resource allocation information for each of the plurality of MSs.
Referring to FIG. 2, channel coder 502 exists in OFDMA transmitter 136. Channel coder 502 converts a data burst obtained from message creation section 126 to a baseband modulated signal. FIG. 3 shows a block diagram illustrating typical channel coder 502. Channel coder 502 is constructed of FEC encoder 304, circular buffer 308, HARQ subpacket generator (bit selection and repetition block) 306, modulator 310 and subpacket generation control section 312.
Referring to FIG. 3, FEC encoder 304 converts a data burst to coded bits using a predetermined coding scheme such as CTC (Convolutional Turbo Coding). The coded bits made up of information bits and parity bits are normally stored in circular buffer 308. The information bits are arranged from the leading part of circular buffer 308, followed by the parity bits. The size of circular buffer 308 for the data burst can be expressed as follows,
                    (                  Equation          ⁢                                          ⁢          1                )                                                                      N          CB                =                              N            DB                                M            cr                                              [        1        ]            Here, NDB is a size of the data burst, Mcr is a mother coding rate of FEC encoder 304 such as Mcr=⅓.
Referring to FIG. 3, HARQ subpacket generator 306 punctures (or repeats) the coded bits in circular buffer 308 to thereby create a HARQ subpacket.
FIG. 4 illustrates a HARQ subpacket generation method at Mcr=⅓.
To create a HARQ subpacket to be transmitted at i-th transmission, HARQ subpacket generator 306 needs to know the starting position (that is, Pi) in circular buffer 308 and the size (that is, Ni) of the HARQ subpacket transmitted at the i-th transmission. The starting position and size are supplied by subpacket generation control section 312.
The starting position of the HARQ subpacket transmitted at the i-th transmission is normally determined by an SPID (subpacket identifier) of a HARQ transmitted at the i-th transmission. Subpacket generation control section 312 determines the size of the HARQ subpacket according to MCS information and resource allocation information and indicates the size to HARQ subpacket generator 306. The MCS information and the resource allocation information are described in the resource allocation control signalling created by resource allocation creation section 134.
Referring to FIG. 3, modulator 310 converts the HARQ subpacket to a baseband modulated signal.
Referring to FIG. 2, channel decoder 504 exists in OFDMA receiver 138. Channel decoder 504 demodulates/decodes a baseband modulated signal received using HARQ soft combining such as HARQ IR (Incremental Redundancy).
FIG. 5 shows a block diagram illustrating typical MS 104. MS 104 is provided with WiMAX and Wi-Fi, and is constructed of WiMAX PHY block 142, Wi-Fi PHY block 144, WiMAX MAC block 146, Wi-Fi MAC block 148 and GLL (general link layer) block 150. WiMAX MAC block 146 executes a WiMAX OFDMA-based media access control protocol. WiMAX PHY block 142 executes a WiMAX OFDMA-based physical layer protocol under the control of WiMAX MAC block 146. Wi-Fi MAC block 148 executes a Wi-Fi CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)-based media access control protocol. Wi-Fi PHY block 144 executes a Wi-Fi OFDM (Orthogonal Frequency Division Multiplexing)/DSSS (Direct Sequence Spread Spectrum)-based physical layer protocol, under the control of Wi-Fi MAC block 148. GLL block 150 has a function of managing coordinated operation between heterogeneous WiMAX and Wi-Fi links.
Referring to FIG. 5, WiMAX MAC block 146 is further constructed of control section 154, message creation section 152 and message processing section 156. Control section 154 controls a general MAC protocol operation. Message creation section 152 creates UL control signaling and a data packet under the control of control section 154. Message processing section 156 analyzes a data packet and DL control signaling received from BS 102 under the control of control section 154 and reports the analysis result to control section 154.
It should be noted that the data packet and UL control signalling created by message creation section 152 is transmitted to BS 102 by MS 104 via OFDMA transmitter 162 in WiMAX PHY block 142. The data packet and DL control signaling to be analyzed by message processing section 156 is received by MS 104 via OFDMA receiver 164 in WiMAX PHY block 142.
Referring to FIG. 5, resource analysis section 151 and HFBCH analysis section 153 exist in message processing section 156. HFBCH analysis section 153 analyzes a received HFBCH in response to UL data transmission and decides whether the corresponding UL data transmission has been successful or not. Resource analysis section 151 analyzes the received resource allocation control signalling and extracts resource allocation information identified for MS 104. In the case of UL data transmission, a data packet created by message creation section 152 under the control of control section 154 is then transmitted by MS 104 to BS 102 according to the extracted resource allocation information.
Referring to FIG. 5, channel coder 402 exists in OFDMA transmitter 162 and channel decoder 404 exists in OFDMA receiver 164. It should be noted that channel coder 402 in OFDMA transmitter 162 has a configuration and function similar to those of channel coder 502 in OFDMA transmitter 136, and channel decoder 404 in OFDMA receiver 164 has a configuration and function similar to those of channel decoder 504 in OFDMA receiver 138.
FIG. 6 shows a block diagram illustrating typical MS 106. MS 106 is also provided with both WiMAX and Wi-Fi, and has a configuration and function quite similar to those of MS 104. Channel coder 602 in OFDMA transmitter 182 has a configuration and function similar to those of channel coder 402 in OFDMA transmitter 162. As shown in FIG. 5, a main difference between MS 104 and MS 106 is that scheduler 158 exists in the Wi-Fi MAC block of MS 104 and this scheduler is used for collaboration scheduling for CliCo.
Referring to FIG. 1, BS 102 communicates with MS 104 via WiMAX links 108a and 108b, and communicates with MS 106 via WiMAX links 110a and 110b. MS 104 communicates with MS 106 peer-to-peer Wi-Fi links 112a and 112b. Alternatively, MS 104 may also communicate with MS 104 using other wireless techniques such as WiMAX, Bluetooth or 60 GHz mmW (millimeter wave).
It should be, noted that CliCo can be realized on both DL and UL of radio communication system 100. In the present invention, the operation of CliCo on an UL (uplink) in radio communication system 100 is taken as an example.
Referring to FIG. 1, when signal quality of WiMAX link 108a between BS 102 and MS 104 degrades, MS 104 can start an UL (uplink) CliCo procedure such as neighbor discovery, cooperator selection/allocation. When signal quality of WiMAX link 110a between BS 102 and MS 106 is good, MS 104 can select MS 106 as a cooperator. In the context of CliCo, MS 104 is called originating MS and MS 106 is called cooperating MS.
CliCo may occur in various situations. For example, if originating MS 104 is assumed to be located at the back of a cafeteria, signal quality of the WiMAX link to originating MS 104 may be quite low. On the other hand, if cooperating MS 106 is assumed to be located much closer to the window or entrance of the cafeteria than originating MS 104, cooperating MS 106 can thereby have much higher signal quality of WiMAX link than originating MS 104.
FIG. 7 shows a diagram illustrating typical frame configuration 200 applicable to a radio communication system that performs the CliCo shown in FIG. 1. Referring to FIG. 7, each of frame 202 and frame 212 is made up of eight subframes. Five of the eight subframes are DL subframes and the rest are UL subframes.
As far as CliCo of the UL (uplink) is concerned, BS 102 can transmit MAP 220 to a plurality of mobile stations connected to BS 102 including originating MS 104 and cooperating MS 106 involved in CliCo in first DL subframe 204 of frame 202. MAP 220 is made up of a plurality of MAP IEs (information elements). Some of the MAP IEs can carry HARQ feedback information for UL data transmission and some other MAP IEs can carry resource allocation information for DL/UL data transmission. One MAP IE in MAP 220 that carries HARQ feedback information forms an HBFCH for UL data transmission.
During period 208 between first DL subframe 204 and first UL subframe 206 of frame 202, originating MS 104 and cooperating MS 106 need to decode MAP 220 to obtain resource allocation information including their respective items of HFBCH index information. Furthermore, originating MS 104 needs to transmit UL data burst 250 to cooperating MS 106 via peer-to-peer Wi-Fi link 112a. 
If originating MS 104 has successfully decoded MAP 220 transmitted by BS 102 via WiMAX link 108b, originating MS 104 transmits a HARQ subpacket of UL data burst 250 to BS 102 via WiMAX link 108a according to the received resource allocation information in first UL subframe 206 of frame 202. On the other band, if cooperating MS 106 has successfully decoded MAP 220 transmitted by BS 102 via WiMAX link 110b and has also successfully received UL data burst 250 transmitted from originating MS 104 via peer-to-peer Wi-Fi link 112a, cooperating MS 106 simultaneously transmits the HARQ subpacket of same UL data burst 250 to BS 102 via WiMAX link 110a according to the received resource allocation information in first UL subframe 206 of frame 202. As a result, BS 102 can perform HARQ soft combining of combining two HARQ subpackets of UL data burst 250 received from WiMAX link 108a and WiMAX link 110a to improve quality of the received signal.
In second DL subframe 214 of frame 212, BS 102 can transmit MAP 240 to a plurality of mobile stations connected to BS 102 including originating MS 104 and cooperating MS 106 involved in CliCo. As described above, HFBCHs which form a part of MAP 240 can carry HARQ feedback information for UL data burst 250 transmitted by originating MS 104 and cooperating MS 106 in first UL subframe 206 of frame 202.
During period 218 between second DL subframe 214 and first UL subframe 216 of frame 212, in order to obtain the respective items of HARQ feedback information for UL data burst 250, originating MS 104 and cooperating MS 106 need to decode their respective HFBCHs in MAP 240 according to HFBCH index information obtained by decoding MAP 220 during period 208.
When the HARQ feedback information indicates in first UL subframe 206 of frame 202 that BS 102 has not correctly decoded UL data burst 250 transmitted by originating MS 104 and cooperating MS 106, originating MS 104 and cooperating MS 106 need to retransmit UL data burst 250 in first UL subframe 216 of frame 212.
According to the IEEE 802.16m draft standard, the specified HARQ transmission mechanism does not deal with UL (uplink) CliCo (see NPL 1). However, the same mechanism is applicable to UL (uplink) CliCo in a direct way.
According to the IEEE 802.16m draft standard, on an UL, a “synchronous HARQ operating mode” in which HARQ timing is performed at a constant interval is used and a “non-adaptive HARQ operating mode” in which the resource size or the like is not changed is used (see NPL 1).
In the synchronous HARQ operating mode, both originating MS 104 and cooperating MS 106 can use the same HARQ subpacket transmission rule as shown in Table 1.
TABLE 1SPIDInitialSecondThirdFourthFifthtrans-trans-trans-trans-trans-missionmissionmissionmissionmission. . .Originating MS01230. . .Cooperating MS01230. . .
According to the subpacket transmission rule shown in Table 1, each of originating MS 104 and cooperating MS 106 transmits a subpacket having SPID=0 at initial transmission and transmits one of subpackets having SPID=0, 1, 2, 3 in cyclic order of retransmission.
According to the IEEE 802.16m draft standard, the resource allocation information is transmitted by BS 102 only at the initial transmission using MAP IEs addressed to originating MS 104 and cooperating MS 106, and this information is also used for retransmission by originating MS 104 and cooperating MS 106 (see NPL 1). That is, this means that the size of the HARQ subpacket is the same for both originating MS 104 and cooperating MS 106 whether in HARQ transmission or in HARQ retransmission.
According to the IEEE 802.16m draft standard, for both originating MS 104 and cooperating MS 106, the starting position of the HARQ subpacket transmitted at i-th transmission is determined as follows (see NPL 1).[2]Pi[SPID(i)·N] mod NCB  (Equation 2)
Here, N is a size of a HARQ subpacket (N=NOM for originating MS 104, N=NCM for cooperating MS 106), N=NRE′ NSM′ Nmod, where NRE is the number of data tones (data units) allocated for transmission of a data burst and NSM is an STC (space-time coding) rate and Nmod is a modulation order. The values of NRE, NSM and Nmod can be obtained from the resource allocation information. NCB is a circular buffer size for a data burst defined in equation 1. SPID(i) is an SPIN of a HARQ subpacket transmitted at i-th transmission.
FIG. 8 illustrates typical HARQ subpacket transmission performed by both originating MS 104 and cooperating MS 106 according to the subpacket transmission rule shown in Table 1 and the rule for determining the starting positions of HARQ subpackets defined in equation 2. In FIG. 8, suppose coding rate Mcr=⅓ and NOM=NCM=⅜·NCB of the FEC encoder.
Referring to FIG. 8, in originating MS 104, the starting positions of the HARQ subpackets in four transmissions including the initial transmission are calculated as follows.P1=0P2=⅜·NCB P3=¾·NCB(= 6/8·NCB)P4=⅛·NCB 
In cooperating MS 106, the starting positions of the HARQ subpackets in four transmissions including the initial transmission are calculated as follows.P1=0P2=¼·NCB P3=½·NCB= 2/4·NCB)P4=¾·NCB 
It is easily understandable from FIG. 8 that individual HARQ subpackets transmitted by originating MS 104 and cooperating MS 106 are created so as to be in the same direction in the circular buffer. Furthermore, the individual HARQ subpackets transmitted by originating MS 104 and cooperating MS 106 apparently overlap with each other even in initial transmission.